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Old 04-08-2006, 04:27 PM   #1
njchen24
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Default Is there any consequence filling 1/2 tank with regular in a 2.5GT?

Greetings:

The pumpist might have some hearing problem while I am specifically asking for Super; he puts regular in my 05 2.5GT tank instead. By the time I realize the mistake, it's almost 1/2 tank (7.5 galons) already and fill up the remaining tank with Super. I wonder if there will be any serious consequence to this error. If so, what will be the worst case scenario?

Thanks in advance for your time and help.
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Old 04-08-2006, 04:29 PM   #2
Hondaslayer
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Drive lightly and avoid boosting it too much.

The ecm will learn around it but your mileage and performance will be hampered.
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Old 04-08-2006, 04:34 PM   #3
demo24
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It will be alright, just don't drive to hard
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Old 04-08-2006, 04:37 PM   #4
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1) wait until your tank is almost completely empty (gas light on)
2) Fill up with highest octane possible
3) Disconnect negative battery terminal
4) Hold brake down for ~10 seconds
5) Reconnect negative battery terminal (may throw a spark or two)
6) Drive around like normal and don't do it again
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Old 04-08-2006, 04:42 PM   #5
andrew_j
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Don't worry about it. Your owners manual clearly states that it can be used in a pinch but not to make it a regular practice.
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Old 04-08-2006, 04:44 PM   #6
Hayes
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No problem. Just wait till the gas is down to~1/2 and refill.
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Old 04-08-2006, 05:21 PM   #7
STimo
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Either drive around without going into boost until your really low and then fill up with 91/93 or you can put in some race gas (motorsport 109) and that will raise the oct. depending on how much you put in.
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Old 04-08-2006, 07:05 PM   #8
Javier
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The same thing happened to me. I went and got a few gallons of toulene and dumped it in my tank. I took it easy for that tank and then filled it up with the proper gas after that.
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Old 04-08-2006, 10:27 PM   #9
njchen24
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Thank you all for your valuable input and advice.

One thing for sure I will yel on the top of my lung "FILL UP SUPER PLEASE" on my next tank.

Lexington:

If it doesn't take too long of your time; could you please explain the purpose of step #3 thru #5? May be it is for resetting the ECM.
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Old 04-08-2006, 10:54 PM   #10
Starkiller
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Its so the ECU unlearns the fuel and timing adjustments it made for the lower octane gas.
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Old 04-08-2006, 10:59 PM   #11
El Gato
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Quote:
Originally Posted by njchen24
Greetings:

The pumpist might have some hearing problem while I am specifically asking for Super; he puts regular in my 05 2.5GT tank instead. By the time I realize the mistake, it's almost 1/2 tank (7.5 galons) already and fill up the remaining tank with Super. I wonder if there will be any serious consequence to this error. If so, what will be the worst case scenario?

Thanks in advance for your time and help.
Get two gallons of C16, mix it and youll be fine.
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Old 04-08-2006, 11:24 PM   #12
kreitz3
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at this point you might as well trade your car in for an STi. It's going to explode.
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Old 04-08-2006, 11:34 PM   #13
problemcat13
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Your car will die!

No, not really. Parts stores around here carry octane booster. You can add that, but mostly I'd just take it easy, don't run it hard. Higher octane means less detonation (so lower would mean more chance of detonation), but as long as you don't run it hard it will be just fine. Probably would be even if you did, as long as you don't have a lot of mods (UP,DP, engine management highly tuned for 93).
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Old 04-09-2006, 12:02 AM   #14
Mike Wevrick
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Quote:
Originally Posted by Starkiller
Its so the ECU unlearns the fuel and timing adjustments it made for the lower octane gas.
It should do that without doing the battery trick.
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Old 04-09-2006, 02:03 AM   #15
blinguskahn
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Quote:
Originally Posted by El Gato
Get two gallons of C16, mix it and youll be fine.
+1. Absolutely the best idea is to just add octane to the tank if your super is 91. If your location was entered in your profile I would be albe to avoid the IF and tell you IF your super is 93 then 1/2 93 and 87 will be safe and you dont have to worry about it.

If your super is 91 than I would worry about it. Yes you can stay out of boost till your are empty and refill but even with straight 91 the 2.5L engine is known to knock. If I were you I would put some race gas or NOS octane bbooster in there RIGHT now. For a full tank go with at least 2 bottles of NOS booster if using race gas do 1 gallon now and when it drains another gallon driving around put 1 more in.

For a good site to calculate your octane mix go to:

http://www.ranney.com/~mjr/fuel_blend.html
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Old 04-09-2006, 09:13 AM   #16
Starkiller
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True, but it will adjust quicker starting from scratch.
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Old 04-09-2006, 12:07 PM   #17
WRXdonkey
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pump your own gas..?

Down here, a true "Full Service" gas station doesn't exist. They just have left over "Full Service" pumps that will charge you $2.50 more per gallon for you tp pump the gas yourself. I've seen guys drop in a few gallons before realizing and get REALLY upset, heheh.
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Old 04-09-2006, 03:37 PM   #18
njchen24
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I am confuse.

NOS booster contains MMT and the manual recommend not to use it. Otherwise it may not be covered by Subaru warranty.

I am missing something?

I went to two autoparts stores (R&S Strauss & Pepboys). Most of the octane booster contains MMT. I get all the octane booster brand that doesn't mention MMT on its label. However, how I can be sure that these products effectively does not contain MMT.

Any additional input is greatly appreciated.

Quote:
Originally Posted by blinguskahn
+1. Absolutely the best idea is to just add octane to the tank if your super is 91. If your location was entered in your profile I would be albe to avoid the IF and tell you IF your super is 93 then 1/2 93 and 87 will be safe and you dont have to worry about it.

If your super is 91 than I would worry about it. Yes you can stay out of boost till your are empty and refill but even with straight 91 the 2.5L engine is known to knock. If I were you I would put some race gas or NOS octane bbooster in there RIGHT now. For a full tank go with at least 2 bottles of NOS booster if using race gas do 1 gallon now and when it drains another gallon driving around put 1 more in.

For a good site to calculate your octane mix go to:

http://www.ranney.com/~mjr/fuel_blend.html

Last edited by njchen24; 04-09-2006 at 03:47 PM.
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Old 04-09-2006, 05:24 PM   #19
Kevex
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you should be ok if it's bone stock, and don't drive too hard.
think about it, an ECU has enough power to correct fuel mapping due to modifications, it should have enough power to correct a few octane lower fuel.
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Old 04-10-2006, 12:35 AM   #20
scrappy doo
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dont get octane booster, just get a higher octane gas. pump your own gas next time! it's like letting a school cheerleading team wash your car for fundraising using a rag they just cleaned a muddy rocky truck with, and then drying it with a old scratchy towel...just remember, if you want it done right....
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Old 04-10-2006, 01:20 AM   #21
Javier
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I'm gonna take a stab in the dark and say that njchen24 is from New Jersey, which means two things:

1) You are not legally allowed to pump your own gas. As rediculous as that sounds, if you've met a large sampling of people from NJ you'd probably think that was a good idea too...

2) Premium is 93octane which means if he did truly go 50/50 on the tank, it's sitting at about 90 octane which isn't a big deal. I would still take it easy though...
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Old 04-10-2006, 06:46 AM   #22
Uncle Scotty
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....w 0 w.....all this kaos over a 1/2 tank of gas.....
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